Field of the Invention
The present invention is related to a scanning microscope, and in particular, the present invention is related to a scanning microscope that includes a focal position adjustment unit configured to adjust a focal position of an objective or a condenser lens with respect to a sample.
Description of the Related Art
In the field of microscopy, various methods have been proposed as methods for adjusting a focal position with respect to a sample, and as one such method, a method of making an objective move in an optical axis direction is known. In general, a microscope that adjusts the focal position with this method is configured such that a revolver to which the objective is mounted and a revolver arm moves in the optical axis direction. Such a configuration is preferable for executing a patch clamp method that uses a relatively large space in an upper side of a stage by using an upright multi-photon excitation laser microscope, for example.
When the objective is made to move in the optical axis direction in a microscope that employs an epi-illumination, vignetting may occur in an optical system between the objective and a detector, due to a change in an optical path length between the objective and the detector. Specific explanations are given for this point, in reference to FIG. 1.
FIG. 1 illustrates a configuration of a multi-photon excitation laser microscope 100 related to a prior art. The multi-photon excitation laser microscope 100 is a scanning microscope that includes an XY scanner 102 at a position that is optically conjugate to a position of a pupil P of the objective 107 on an illumination optical path (hereinafter called a pupil-conjugate position) and a photomultiplier tube (hereinafter called a PMT) 109 as a non-descanned detector (also called an NDD) at a pupil-conjugate position of the objective 107 on a detection optical path. A relay optical system 103 is an optical system that relays the pupil P of the objective 107 to the XY scanner 102. A relay optical system 108 is an optical system that relays the pupil P of the objective 107 to the PMT 109.
In the multi-photon excitation laser microscope 100, fluorescence generated from a sample S by irradiation of laser light L1 (a dotted dashed line in FIG. 1) that has been emitted from a laser light source 101 is converted by the objective 107 into a parallel light flux. After that, the fluorescence is reflected on a dichroic mirror 104, and is incident to the PMT 109 through the relay optical system 108.
When the objective 107 is made to move in the optical axis direction to adjust the focal position in the multi-photon excitation laser microscope 100, the dichroic mirror 104 does not move, while the revolver 106 and revolver arm 105 move together with the objective 107 in the optical axis direction. Consequently, a distance from the objective 107 to the dichroic mirror 104 changes.
A light flux L2 (a dashed line of FIG. 1) on an optical axis of fluorescence emitted from the objective 107 parallel to the optical axis is incident to the same position of the dichroic mirror 104, even when the distance between the objective 107 and the dichroic mirror 104 changes. On the other hand, an off-axis light flux L3 (a dotted line of FIG. 1) of fluorescence emitted from the objective 107 at an angle with respect to the optical axis deviates from the dichroic mirror 104 when the distance between the objective 107 and the dichroic mirror 104 becomes too long, and vignetting is likely to occur.
Technologies of suppressing the occurrence of the above mentioned vignetting due to the adjustment of the focal position are disclosed, for example, in Japanese Laid-open Patent Publication No. 2009-181123 and Japanese Laid-open Patent Publication No. 2008-197127. Japanese Laid-open Patent Publication No. 2009-181123 discloses a configuration in which a decoupling unit and a detector are provided between the objective and a guiding unit that is necessary for focusing an objective exchanger (paragraph [0009] of Japanese Laid-open Patent Publication No. 2009-181123). In such a configuration, since the entire detection system moves together with the objective when adjusting the focal position, the optical path length from the objective to the detector does not change and vignetting is not likely to occur.
Japanese Laid-open Patent Publication No. 2008-197127 discloses a microscope objective that includes an optical path division means and a detector (paragraph [0010] of Japanese Laid-open Patent Publication No. 2008-197127). In such a configuration, since the detection system is provided in the objective, a distance from a sample (i.e., a focal position) to the detector is always constant, and therefore, vignetting is not likely to occur.